1. Field of the Invention
The present invention relates to a metal tubing which is made of a carbon steel or stainless steel and having a diameter less than about 20 mm and a wall thickness less than about 1.5 mm and which is frequently used as a passage for supplying oil or air in an automobile, machine, equipment, apparatus, or the like and, more particularly, to an improved structure of the end of such a relatively thin-walled tubing of a relatively small diameter which is coupled to a flange by welding.
2. Description of the Prior Art
The manner in which a conventional structure of this kind is fixed to a flange by welding is next described by referring to FIG. 3. The connected end portion of a tubing P' is directly inserted into a hole 12 formed in a flange 11 shaped like a plate or board. Then, the end portion of the tubing is manually heated using a gas burner or the like to weld it to the inner wall 13 of the hole 12 at locations 14.
This prior art structure has some disadvantages. Specifically, because the connected end portion of the tubing P' is directly inserted into the hole 12 in the flange 11 and welded at 14, and because of a quite large difference in wall thickness between the tubing P' and the flange 11 and the manual heating operation using the burner, the tubing P' and the flange, especially the tubing P', are often locally overheated to melt a part of the tubing, resulting in a thin-walled portion 15 as shown in FIG. 4. This reduces the mechanical strength of this part. Also, the shape varies from product to product when bent. Further, when the structure is used under undesirable conditions, if it is connected to a base or subjected to vibration, then the portion of the tubing P' which was heated is cracked or broken or causes leakage while it is in use.